Schools should teach children in single-sex classes to over-come the "laddish" culture that stops boys learning, according to a major Government research project.

The study found teaching boys and girls separately for some subjects helped boys concentrate on their lessons and score better exam grades.

But academics at Cambridge University's faculty of education warned that beating the "macho" culture in secondary and even primary schools would be crucial for improving results.

The Department for Education commissioned the four-year project involving 50 schools to try to close the gap between girls and boys.

Every year girls out-perform boys at GCSE and in primary school tests, with few signs that the gender gap is narrowing.

The latest research found that single-sex classes for some subjects could be a powerful tool in helping boys do better at school - as well as benefiting girls.

Led by Mike Younger and Molly Warrington, the researchers said: "Many girls and boys feel more at ease in such classes, feel more able to interact with learning and to show real interest without inhibition, and often achieve more highly as a result."

Some single-sex classes have developed problems, however, as groups of boys set up a "macho regime" which alienated others in the class.

But overall, the academics concluded: "Evidence in favour of the development of single-sex classes for some subjects, from both students' voices and from an analysis of levels of academic achievement, is nonetheless persuasive."

The report warned that in some schools the activities of "macho" boys, who were influential in their year, stopped the rest of their classmates from working.

"It is self-evident, not only in secondary, but also in primary schools, that some boys go to considerable lengths to protect their macho image and their sense of self-worth by indulging in a range of nonconformist behaviour which frequently prevents them and others in the same classes, from achieving well."

This disruptive behaviour was particularly damaging from boys who were "key players" in their year.

The academics recommended schemes that targeted "those students whose physical presence, manner and behaviour exerted considerable power and influence within the peer group".

Older boys were also encouraged to help teach younger children to read, thereby boosting their own self-esteem as they took on the role of reading "experts".